The present invention relates to a method and apparatus for data communication through a composite network. More particularly, the invention concerns a data communication method and apparatus suited advantageously for a system in which an information collecting center connected to a certain network collects information from a plurality of work stations connected to another network.
In recent years, communication networks of various types, such as a digital data exchange network (hereinafter referred to as DDX in abbreviation), a value-added network (hereinafter referred to as VAN), a local area network (hereinafter referred to as LAN) and the others have been developed for various practical applications. Further, there has been realized a composite network which is constituted by interconnecting these various types of networks. A typical one of the hitherto known data communication systems based on the composite network concept is illustrated in FIG. 2 of the accompanying drawings.
In FIG. 2, a reference numeral 10 denotes a first network constituted by an external fee-charging network such as, for example, a DDX network designed for packet transmission, 20 denotes a second network such as a LAN. Both networks 10 and 20 are interconnected through an inter-working unit or IWU 200. Assuming now a network system in which an information collecting center 100 including a host computer or the like is connected to the first network as a terminal and in which a plurality of work stations exemplified by 310, 320 and 330 are connected to the network 20, consideration is made as to a manner in which the information collecting center 100 collects information from the work stations 310, 320 and 330. On the assumption, by way of the external network 10 which charges a fee in accordance with the amount of data for transmission, the information collecting center 100 issues an information collection command 50 first to the work station 310 to receive response information 55 from the station 310 in response to that command 50, after which the information collecting center 100 issues an information collecting command 60 to the work station 320 and receives response information 65 from that station 320, and finally the information collecting center 100 issues an information collecting command 70 to the work station 330 to receive therefrom the response information 75. The information collecting center 100 is typically imparted with a function to manage or supervise a number of the work stations.
The prior art system described above encounters no material problems so far as the transmission and reception of information are performed between the information collecting center and other work stations within the same network. However, a promising tendency will be seen in the information exchange performed through a composite network constituted by a plurality of networks interconnected to one another. In this connection, the prior art system in which the information collecting center issues commands separately and individually to each of the work stations on the one-by-one basis by way of a plurality of networks will require that a number of commands corresponding to that of the work stations have to be transmitted through the plurality of work stations enroute to the object station, involving a non-negligible increasing in the charged fee as well as the traffic. By the way, the data communication method through a composite network is proposed in N. C. Strole's article entitled "How IBM addresses LAN requirements with the token ring" of "Data Communications", February 1986, p.p. 120-124.